A polymeric rubber elastic body essentially has either a soft polymer structure or a structure consisting of a rigid polymer system combined with a soft polymer system, and is used in a wide variety of industrial fields because it has rubber elasticity at ordinary temperatures and it can be mechanically molded due to its plasticization at high temperatures similar to thermoplastics. Typical polymeric rubber elastic bodies include those based on styrene, olefin, polyester, polyurethane, polyvinyl chloride, and polyamide. These polymeric rubber elastic bodies are usually provided as molded articles produced by mechanical operation such as extrusion molding, and when used in coating agents for various materials, adhesives, binders, modifiers such as emulsions, or binders for fibers, the polymeric rubber elastic bodies are used desirably in the form of aqueous dispersions.
Aqueous dispersions of polymeric rubber elastic bodies have been extensively examined, among which an aqueous dispersion of a styrene rubber elastic body has been provided as a practical product. The aqueous dispersion of a styrene rubber elastic body is produced usually by mixing an organic phase containing a styrene rubber elastic body dissolved in an organic solvent, with an aqueous phase containing an emulsifier (surfactant) dissolved in an aqueous medium, and emulsifying the mixture with a homomixer or the like, followed by removing the organic solvent (see, for example, JP 51-23532 A and JP 2003-253134 A).
However, molded articles obtained from the aqueous dispersion of a styrene rubber elastic body are generally inferior in abrasion resistance, flex resistance, oil resistance, and weather resistance. A polyamide rubber elastic body, on the other hand, can produce molded articles not only excellent in these properties but also excellent in transparency, flexibility, impact strength, tensile strength, chemical resistance, and heat resistance, and further has an advantage that its molded articles can be made thin-walled because it has higher stress upon deformation than other polymeric rubber elastic bodies of the same rigidity, and is thus useful for example as a material for producing packaging films, automobile parts, sporting goods, and medical devices. Accordingly, an aqueous dispersion of polyamide rubber elastic body has been desired to be realized as there has been no example of practical application thereof.
An object of the present invention is to realize an aqueous dispersion of polyamide rubber elastic body capable of producing a molded article having the characteristics of the polyamide rubber elastic body, particularly a molded article which hardly suffers from bleeding of a surfactant and is excellent in transparency.